Optical angle measuring system



Dec. 18, 1951 l. L. CUNNINGHAM OPTICAL ANGLE MEASURING SYSTEM 6 Sheets-Sheet 1 Filed Jan. 12, 1948 /rwi/7 Lamar Cunnihgham Dec. 18, 1951 l. L. CUNNINGHAM OPTICAL ANGLE MEASURING SYSTEM 6 Sheets-Sheet 2 Filed Jan. 12, 1948 xiii/1,1216%.

lrw/n Lamar Cunningham Dec. 18, 1951 l. L. CUNNINGHAM 2,579,067

OPTICAL ANGLE MEASURING SYSTEM Filed Jan. 12, 1948 6 Sheets-Sheet :5

I53 #2 a /4/ a 0 M5 /rw/'n lamar Cuhningham INVEN TOR.

ATTORNEYS l. L. CUNNINGHAM OPTICAL ANGLE MEASURING SYSTEM wwflm 1 I5 'lllllllll'llllllll] o 5 Dec. 18, 1951 Filed Jan. 12, 1948 /m /'/2 Zkmar Canning/7am INVENTOR.

BY r m; Z W

ATTORNEYS Dec. 18, 1951 l. 1.. CUNNINGHAM 7 2,579,067

OPTICAL ANGLE MEASURING SYSTEM Filed Jan. 12, 1948 l 6 Sheets-Sheet 5 71% /rw/'/7 Lamar Cunningham 73 7 INVENTOR.

A TTORNE YS Dec. 18, 1951 l. CUNNINGHAM 2,579,067

OPTICAL ANGLE MEASURING SYSTEM Filed Jan. 12, 1948 i 6 Sheets-Sheet e Jig/ (49 /rw/'n Lamar Cunningham r j gozz I a m;

My! 7 101 WE INVENTOR.

/0 V /08 1W /08 2E0 20 I I Patented Dec. 18, 1951 UNITED STATES-PATENT OFFICE OPTICAL ANGLE MEASURING SYSTEM Irwin L. Cunningham, Odessa, Tex. Application January 12, 1948, Serial No. 1,736

6 Claims. (c1.,ss 1) .This invention relates to new and useful improvements in optical measuring systems, and in'particular to such systems as applied to surveying instruments.

A particular object of the invention is to provide an improved optical measuring system adaptable to the measuring of horizontal and vertical angles which is simple and convenient in operation.

A further object of the invention is to provide an improved surveying instrument which may be very accurately set upon a zero reading while trained upon a first point of observation and then very accurately set upon a second point of observation so as to measure the horizontal or vertical angle between said points with a high degree of accuracy and eliminating the necessity for addition or subtraction of the two readings obtained for the determination of the angle observed.

Another object of the invention is to provide an improved optical measuring system for the measurement of angles, which system may be set upon a zero reading with great accuracy while being trained in any desired direction.

' A still further object of the invention is to provide an improved surveyors instrument in which the operating parts are contained within a substantially weatherproof housing.

Still another object of the invention is to provide an improved optical measuring system employing a fixed and a movable support with observing means carried by the movable support and observed indicia rigidly connected to the fixed support so as to be immovable with respect thereto.

Yet another object of the invention is to provide an improved surveyors instrument having a calibrated measuring disk which may be'caused to rotate with the sighting portion of the instrument or locked into a non-rotative position so as to remain stationary with respect to the support of said instrument.

A further object of the invention is to provide an improved surveyors instrument having an optical measuring system with provision therein for compensating for any inherent errors, or errors arising through operation of the instrument with additional means in the system for causing indicia carried thereby to become alined at any desired point with means for measuring the degree of adjustment necessary to obtain such alinement.

An important object of the invention is to provide an improved surveyors instrument employ measurements.

ing an. optical measuring system having 'provision for obtaining-a proximate reading of the angle being observed, and an expanded Vernier means for efiecting extremely accurate angular A particular object of the invention is to provide an optical measuring system for the meas-.

urement of vertical and horizontal angles employing a calibrated. disk from which a plurality of readings are taken and superimposed one upon the other, such readings coinciding at certain known angles, with provisions being made within the system for measuring with extreme accuracy the angular movement required to bring said readingsinto alinement whereby the angular reading may be determined with relatively great accuracy.

A still further object of the invention is to derstood as forming part and parcel of the intent and purposes ofthis invention.

A construction designed "to carry out the invention will be hereinafter described together with other features of the invention. The invention will be more readily under stood from a reading of the following specification and by reference to the accompanying drawings, wherein examples of the invention are shown, and wherein: a

Fig. 1 is a side elevation, with the lower portion thereof broken away, of a surveyors instrument constructed in accordance with this invention,- 1 1 N Fig. 2 is a vertical, sectional view of the lower portion of the instrument shown in Fig. 1, and showing the measuring plate in a raised position, r

' Fig. 3 is a plan view of the measuring plate housing, with said plate removed, and showing the raising and clamping mechanism,

Fig. 4 is a side elevation of the measuring plate housing, partially broken away to illustrate the clamp adjusting means,

- Fig. 5 is a vertical, sectional view of the measuring plate housing with the plate and clamping means removed to illustrate the arrangenient of the plate raising device,

Fig. 5 is an enlarged, isometric view of aporplate broken away and the measuring disk re-x: J

moved to illustrate the construction of the disk raising mechanism,

Fig. 11 is a view similar to Fig. 10 and illustrating the clamping mechanism, and showing another position of the disk raisir'rgmeclianistn;

Fig. 12 is a view similar to Fig. 9 and takemat i right angles thereto withthe measuring disk and meaursing cylinder removed,

Fig. 13 is an' isometric viw' of'i'thevertical angle me'a'sur'in g structure,

Fig; l4" is" a horizontal, cross-sectional View" takeirtl'irough the verniermeclianism'ofthe ver= ticalangle measuring structure,

Fig.1'5"is afragment'ary; perspective, schematic view'illustrating the optical system;

16*isan"enla'rged perspective'of 'a portion" oftlie measuring cylinder raising device,

Fig; 1*? is" an illustration of a fragment' of the directrea'ding vertical angle scale,

Fig 18' anillustration" oithe right-hand" Vernier scale employed in the modified form of the invention;

Fig-T19 is an illustration-ofairagmentof the direct reading scale for right-hand horizontal angles employed in the-modificatin'of'thein venti'on;

Fi'gi' 20 1s anillustration of "the reading ontained from -the=measuring=plate for alright-hand angle as employed'in the mo'dified fo'rrn of'the invention; and with the=indicia'-'outofalinementf Fig: 2 1 is-a view'similar-to'Fi'g: 20 with the indicia, alined;

Fig; 22 is an illustration of the left liand'vernier' scale;

' Figs 23 is an illustration: of "anfiagment 'of the direct readi'n'g scale for left-Hand angls= em"* ployed in-the modified form;

Fig? 24 is avi'w similar 'tc' Figf 20 and representing therea'ding for a left-hand angle, and" Fig? i's-a'viewsiinilar toFi'g: 21' and representing the reading'for a'left h'an'd angle;

the drawings, the numeral IIJ designates an enlarged internally screw threaded cap adapted to fit upon the uppei 'end oftlier usual surveyors" tripod (not shown) for supporting a tli'eodolite or other surveyinginstruments; The cap Illc'arri'esa ball"- socket" at' it's center', said: socket receiving the usual ball l2 to form' aunt vers'al mounting. A tapered 'spindle? I3 is provided with-an axially extending; screw-threaded stud l projecting from it's-lower end} said" studv engaging within the ball I2 and serving to clamp asup pr'ting p1ate l5 between thef'bottom' of. the spindle" |S and the 'uppe'r'end of said ball. The. plate I5 carries- L -shaped levellingarms I6, and suitable level-ling screws? l -I' extend between said arms-I-a'nd thetupperrsurfaceiof 'the cap'ltfl. Em! ploying this structure; the" levelling: screws H maybe adjusted' 'to: causei thei'rball: |2-.- to revolve wit n tl'i'esocket l iiandttli'ereby'aline the spindle 3 =in a verticaliposition. This structurezis; usual in this type of instrument-and; n'ofclaim' ism thereto.

The spindle I3 is provided with the usual circumferential groove l8 at its medial portion, and has its upper end reducedto form a square, upstanding stud |9. A screw-threaded pin 20 extends vertically and axially from said stud.

A wide, shallow measuring plate housing 2| is adapted to be mounted upon the spindle l3. The housing 2| is in the form of a wide, shallow cone having-,its concave side. directed .upwardly and. carrying a divergent, conicalboss: 22; projecting axially from its underside. The boss 22 is provided with an internal, tapered bore 23 within which the spindle l3 has a snug sliding fit, the

'lower extremitvoiJthe boss 22 being positioned adjacent the upper surface of the plate I5. When the housing is so positioned upon the spindle;.the-;square1.-stud H] of said spindle projects into the interior of said housing and is surrounded by an annular bearing face 24 which may be machined or otherwise suitably formed upon the-bottom interior surf ace of the housing.

As' show-n'= in2Figs. 1"" and"2; this bearingsurfaceii 24 1s raised slightly from the inner wall or bot tom of the housing and is in-horizontal aline ment with the lower boundary'of thestud l9.

A washer- 25' is provided with' a central, square; opening: 26 which snugly. receives the square-2 stud" l9; the. underside oft said washer. being adapted to engage the bearing surface.24 and:cone fine'the boss 22 of thehousing 2| uponithe spindle I37 A central recess 21. isriformed'tirLthe-"upper surface-iof the washer 25' andi'receivesa nuti28? which; engages the screwethreaded'i pin 20.: to: re"-.

openingr26, the washer-25 is heldagainst rotaw tion: with respect-to the spindle and thus with= respect; toxthe tripod upon; which 1 the instrument;

iszzheldz; Howeventhe housing '2'l1'isfree-to roetate upon said spindle,

A'. suitable; circular: measuring: plate or:disk;29 is.a disposed; within the housing abovei-the-iwashen 255. The plate carries. a cylindrical, depending; stub: axle 30;;whioh engagesrwithin a.cylindricalwell." 3|? extending axially and downwardly through-the:- pin 20 and the stud l9, into the spindle: |3'.. The; axle Silrhas a snug sliding fit: within the?wel1.3| soa'svto permit the, plate .29v to rotate-:freelvbutttoprevent lateralmovement" on-displacement:of'- said'plate. This mounting alsmpermits vertical movement of the plate since the: axle- 36 may undergo vertical movement withinathewell 3|.

Initslower position, the plate 29"rests upon th'e'upp er: surface of the washer 25, such engage ment being frictional in nature but sufficient to prevent annular movement of the plate with respect to-the-washer. and thus withrespect to the:=tripo.d.; To, enhance such ,frictionalengagement-, theaplate2:is.urgedtdownwardly by a spring pressed pivct: pin 32.;ca-rrieddn: the center. of a. top? plate 38- which, encloses the upper sidegof; the housing 2|. Beingspring-pressedthe pin 32- willpermit upwardmovement .otthe plate 29, but normally urges saidplatedownwardly into en gagement withthe' upper side of the washer 25. The pin also aids in centering 1 and steadying the plate in-thecourse of suchrevolution as the. latter may; undergo.

The: plate-29- carriessuitable; angular. measur ing indicia' 34 upon itsupper surface, said indicia. being. positioned; upon. the marginal; portion of, the plate. The indicia. issaranged in. a, right and, left-hand limb upon. the upper marginal portionxof theplate. Thus, commencing. at the, zero,

point, the plate is marked ofi in right and 1am-- hand scales indicatingdegrees or fractions of degrees, said scales extending in right and lefthand directions from the zero starting point until they meet at 360 at said starting point. This marking or calibration of a surveying instrument measuring plate is usual and customary, provides two complete 360 scales extending, one in a right-hand direction and one in a left-hand direction. For the purpose of reading thesescales, a pair of diametrically-opposed windows 35 are cut in the top plate 33 near the marginal por-- tion thereof. So positioned, the windows permit observation of the marginal scales appearing upon the plate 29, and also observation of a pair of diametrically-opposed vernier scales 36 secured to and within the housing 2! immediately below said windows. The vernier scales 36 are arcuate in shape and thus conform closely to the periphery of the plate 29. The vernier plates 36 carry theusual vernier scales 3! which permit reading of an indicated angle to a fraction of a degree, and interpolation-of this reading to a still smaller fraction of a degree.

' The usual observing. telescope 38 is pivotally mounted upon trunnions 39 carried at the upper end of a pair of bipod supports 46 which are formed integrally with and extend upwardly from the cover plate 33. The telescope carries the usual level indicator 4| suspended on brackets therefrom. With this structure, the telescope may be swung in a vertical are upon the trunnions 39, or may be rotated in a horizontal plane by rotating the housing 2|.

For rendering the housing rotatable or non-' rotatable with respect to the spindle I3 andthe tripod upon which the instrument is carried, an annular clamp 42 is positioned within the interior of the housing so as to encompass the lower outer periphery of the washer 25. The clamp 42 is of the split ring type having a pair of radially extending ears 43 adapted to be urged together by a suitable screw-threaded bolt 44 so as to compress the ring into a clamping position or expand the ring into a non-clamping position. An actuating rod 45 extends slightly upwardly at an angle and through the bottom of the housing 2|, and has its inner end connected in a universal fashion to the bolt 44. Theouter'end of the rod 45 projects below and beyond the housing and carries a suitable handle or knob 46 upon its outer extremity. In this fashion, the handle 46 may be rotated in either direction so as to actuate the belt or screw 44 and thus tighten or loosen the clamp 42 upon the washer 25. The universal connection between the operating rod and the bolt 44 permits the clamp freedom of circumferential movement in tightening and loosening without necessitating lateral shifting of the rod as the ears 43 move radially during operation of the clamp. Such provision allows the rod to have a relatively tight and weatherproof fit with respect to the bottom of the housing 2| with the consequent advantages resultant therefrom.

Diametrically-opposed from the ears 43, the clamp 42 carries an elongate, radially-extending arm 4'! which projects contiguous to the bottom of the housing 2| to a point near the marginal portion thereof. The outer end of the arm 4'! is bent downwardly to form a finger 48 which projects'through a's1ot'49 in the bottom of the housing, said finger extending a short distance below the underside of said housing. An elongate tubular boss 50 having one endclosed, is

6- afixed to the underside of the housing 2| in ver tic al'alinement with the slot 49, said boss being positioned horizontally and extending perpendicular to the axis of the arm 41. is confined within the enclosed end of the boss and urges a plunger 52 into engagement with one side of the finger 48. The plunger 52 has its end which engages the finger in the form of a relatively short cone whereby frictional re-' sistance'bet'ween these two elements is reduced. An elongate, screw-threaded, adjusting screw 53 is carried within the opposite end of the boss 50 and has its conical tip 54 engaging the opposite side of the finger43 so as to confine said finger between the plunger 52 and the inner end of the adjusting screw 53. A suitable handle or knob 55 is provided upon the outer end of the adjusting screw 53, said knob permitting rotation of the screw for adjusting its position within the boss 56 and thus the position of the inner tip 54 of said screw with respect to the opening orfslot 49.

The plunger 52 serves merely to hold the finger 48 in engagement with the screw 53, this engagement holding, by means of the arm 4?, the clamp 42 against rotation with respect to the housing 2 I. When the clamp is in its loosened or released position, it does not engage the washer 25 and thus the clamp and the housing are free to rotate with respect thereto. However, when the clamp is tightened about the washer 25, it serves to anchor the housing to said washer and thus prevent the rotation of the housing with respect to the tripod upon which the instrument is sup-- ported. After the clamp has been tightened, the adjusting screw 53 may be employed to effect delicate and fine adjustments of the angular position of the housing with respect to the clamp 42 and the washer 25.

As before pointed out, when the measuring plate 29 is in its lower position, it engages the upper surface of the washer 25 in a frictional manner and is thereby held against rotation with respect thereto. It is desirable to provide means for liftingthe plate from engagement with the washer so as to permit the rotation of the former with the housing 2|. To effect this vertical movement, an annular raising ring 56 is positioned within the housing above the clamp 42 and encircling the upper portion of the washer 25. The raising ring 56 does not at any time engage the washer or the clamp, and is normally free to rotate with respect to said washer.

\ A pair of diametrically-opposed springs 51 have their inner ends suitably embedded or affixed to diametrically-opposed points upon the raising ring 56, said springs being relatively long and wide, and having their outer ends embedded, or otherwise suitably affixed to the bottom of the housing 2 I. This structure is best illustrated in Figs; 3 and '7 which show that the springs 51 extend in a substantially horizontal plane within the interior of the housing 2| with their fiat sides facing upwardly and downwardly therein. Being relatively thin, the springs do not occupy an appreciable proportion of the vertical space within said housing, but, being securely afilxed both to the housing and to the raising ring 56, prevent rotation of said ring with respect to the housing. At the same time, the springs are adapted to undergo :a considerable degree of curvature in a vertical are which permits the ring 56 to move vertically within the housing while being so prevented from rotation. To pre-' vent interference with the operation of the ad--' A spring 5|.

J stine; arm. 4 f. he. lamp 42, the longi dinal axisof the springs 51 displaced approximately item the longitudinal axis of said arm.

A second pairof diametrically-opposed springs 53 are: secured to the ring 56 approximately 90 from the springs 51. The springs 58 are of the b-Qwed, leaf type and each has one end secured to the periphery of the ring 56 similarly to the springs 51. The springs 58 are doubled upon themselves and have their opposite ends embedded or otherwise affixed to the inner wall of the housing 2i adjacent an annular bearing surface 59- upon which the clamp 42 rests and which is disposed concentrically with respect to the, bearing surface 24. Being of the bowed type, the springs constantly urge the raising ring 56 upwardly with respect to the housing 2| and the washer 25. They also supplement toa con-- siderable degree the action of the springs 51. inpreventingthe ring 56from rotating with respect o. said o s The raising ring carries a pair of diametri cally-opposed, depending, L-shaped fingers 60 having theirlower portions directed radially outwardly so as to underlie the upper portions of the springs 58. A U-shaped yoke 6| is pivotally mounted upon suitable ears 62 carried by the bottom wall of the housing 2| so as to be disposed. in a substantially horizontal plane within said housing. The yoke 6;! straddles the ring 56; and has each of its arms 63 engaging betweenthe laterally-extending portions of one of the fingersfiii and the upper portion of one of the. springs 58;. Upon downward swinging of the arms about the ears- 62, the fingers 60 are engaged and the ring; 56 is urged downwardly. Similarly, as the arms 63 are swung upwardly in a. vertical arc, the springs 58 are allowed to move the ring 56 in an upward direction.

An. actuating rod. 64 extends through the inclined bottom. of the. housing 2! and-- carries a suitable handle 65 upon its outer end. The inher end of: the rod 64. engages one of; the armsv 63.01 the yoke 6! at a point betweenone of, the;

pivot ears. 6'2 and. the outer extremity of said arm. The engaged arm is enlarged} at the point of'engagement and. carries a transverse window 66 which receivesa cam tip 6]: provided uponv the inner end; of the rod, 64. The can! 61 is sub.- stantially rectangular in outline and. thus, is. adapted: to permit limited vertical movement of" the arm and thereby the yoke 6! upon rotationits lower'position and: the measuring plate 2.3.:

thereby lowered into frictional engagement; with thew her p a ns' the yoke B. he: r n s. moved pwar y n au es: heip aez Z8 toibe raised within the housing- 2land liftedfrom. engagement with. the was-her 25.

The measuring plate carries an. annular. raisedribor abutting-surface 68=upon its upper surface The rib 68 is arranged concentrically upon the. surface of-the plate and spaced. cute.

wardly'a. considerable distance from the. center thereof so, as to, beadjacent. the scales 3.3, pro, vided: upon. the marginal; portion. of said plate-., In. its raised posit-ion, the; ribabuts the under-..

sideflot the cover plate. 32 in a. frictional. man

men so s to ai r v n i r a io of t e.

measuring plate with respect to the housing. For further aiding in preventing rotation of the measuring plate, the raising ring 56 is pro. vided with a, pair of diametrically-opposed: knife edges 69 upon its upper surface. The; knife edges 69 extend radially of the ring and are positioned one above each of the points of engagement of the raising ring with the springs 57. Being radially disposed upon the raising ring, the knife edges, when engaged with'the underside of the measuringplate 23, exert a maximum restraintupon rotation of said plate with respect to said raising ring. Since the raising ring is securely held against rotation with respect. to the; housing by means. of the two pairs of springs 51 and 58, the measuring plate is thus very securely held against rotation with respect to said housing. In addition, the knife edges prevent rotation of the plate in the QQurseof its short travel from its lower to. its upper position, since the knife edges engage the plate prior to and during such limited verti-- cal movement.

In the operation of this instrument. and the utilization of this measuring system, the instrument is first set up at the desired location and: suitably leveled by means of the screws ll. The handle 65. is rotated to revolve the rod 64 and move the measuring plate 29 into its lower positionwherein it engages the upper surface of the washer 25 and. is thus held against rota.- tion with respect to. the surrounding terrain. In this position, the measuring plate may be considered as fixed or immovable, and its posi-' tion with relation to the housing 2i alteredflor varied by means of loosening the clamp :22 and revolving the housing about said plate.- Such revolution is continued until the zero line on the scales 34 carried by the measuring plate alines in proximate fashion with the zero line of the desired Vernier scale 31". Following this, the clamp 42 may be tightened and final and minute adjustments of the housing with respect to the measuring plate made by adjustment of the screw 53 which causes the housing. tov shift slightlywith respect to said clamp 42.-

Havingthus set the measuring plate at zero with respect to-the housing, the former may be raised through actuation of the handle 65 and; the yoke 6| so that the plate is'held immovably withrespect to the housing. Then the clamp 4-2- may be released and the housing revolved to-bring the telescope 38 to bear upon the first. sighting point. During such revolution, it is to be noted, the. measuring plate remains set ex.- actly at zero withrespeot to the housing. Having brought the housing into a position wherein. the telescope, which normally contains or carries cross hairs or av reticule. (not shown), into proximatealinement with the object representing. the first; sighting point, the clamp 32: may again be, tightened and; the angular position of the housing; adjusted by the screw 53' to bring the, reticulein exact alinement with the before mentioned first sighting point. Upon completion of these steps; the zero line of the measuring plate has been aimed with exactness: with the first sighting point, andthe operator is ready to make an actuaLmea-surement;

The; measuringplate 29 is now moved tov its. lower: position,vv through. actuation; of: the handle: 1 and the yoke; 6|. After; thisstepy the: plate is held immovable with respect to the tripod and. thus; with respect to; the surrounding terrain; and the firstsighting; point. The. clamp; is re..-.

- mits very close readings of observed angles.

leased and the housing then revolves until the telescope is approximately alined with the second sighting point which may be displaced a considerable angular distance from the first sighting point. Upon again tightening the clamp 42, and making minute adjustments with the screw 53, the telescope, and therefore the housing may be brought into exact alinement with the second point of observation, and an accurate determination of the angle measured be efiected by a reading of the indications upon the scale 34 of the measuring plate and the scale 31 of the Vernier. At the same time, the opposite or 180 angle may be read by means of the diametrically opposed Vernier.

If additional accuracy is required, the reading fof the observed angle may be doubled so as to reduce the subjective error. Such doubling of the angle may be accomplished by raising the steps, the reading of the angle obtainedis now alined with the first point of observation. The

plate 29 may now be lowered and the clamp released so that the telescope can again be swung to the second point of observation. Here,

again, the clamp is tightened and an exact alinement of the telescope with the second point of observation obtained by means of the adjusting screw 53. The reading now taken from the in strument represents twice the measured or desired angle reading with the consequent reduction in subjective error.

.Of course, if desired, the plate 29 need not be set at'zero at the beginning, but a reading may be taken'and recorded as a'zer'o reading. Such reading is later to be added or subtracted to or from the final reading as the case may be. Right and left-hand angular measurements 'aremade in the usual fashion by reading the applicable scale by means of the particular vernier in use. At the same time; the opposite reading may be obtained from the second Vernier scale.

The structure illustrated and described eliminates to a substantial degree'many of the objective errors present in" this type of instrument by reason of its rigid and exact structure. At the same time, it prevents many of the subjective errors which arise since provision is made for shifting the measuring plate so that its zero line coincides with any desired point. Unintentional errors in reading angles and in calculating the actual angle observed are thus reduced to a substantial minimum. In Figs. 8 through 21 of the drawings, a modifled form of the invention is illustrated. This modification employs an optical system of measurement which is extremely accurate and per- At the same time, this modification incorporates the basic principle of the first form described which permits the shifting of the measuring plate or cylinder so that its zero line coincides with any desired point.

The modified form of the invention employs the cap l supporting the base plate 15 and utilizing the adjusting screws I! in the same fashion as the first described form of the invention, these elements being similar in all material respects to those described hereinbefore. 'The base plate l carries the spindle 13 having a and holds saidwasher against rotation with respect to the spindle H3; The washer carries a central recess 11in its upper surface, saidrecess I accommodating a lock nut '18 which engages the screw-threaded pin and retains the washer-in position upon the stud I9; The boss 13 of the housing is thus retained between the under side of the'washer and the upper side of the bottom or supportplate [5. Again, the boss I9 is surrounded by an annular bearing surface 24 against whichtheunder side of the Washer 15 bears and whichpermits rotation of the housing with respectto said washer.

' periphery of'the'opening 8|.

to the spindle l3.

An "external, annular flange 19 is formed upon the washer l5 and adapted to receive 'a'transof glass or plastic or any other suitable or similar 'material. The plate is circular in shape and has acircular opening 8| cut in its central'portion, the opening 8| receiving an upstandinga'nnular flange 82carried upon the upper surface 'of the washer 15. Suitable adjusting screws 83 extend radiallyoutwardly through the flange 82 and have their outer ends engaging the inner By regulation and adjustmentof the screws 83, the plate 80 may be concentrically positioned and .alined with'respect Suitable retaining bolts 'or screws 84'extend' downwardly through the inner margin of the plate 80 into the annular "flange l9, there'being a circular washer or gasket '85 confined between the upper side of said flange and the under 'side ofthe plate. Thus,- by'adjustingth'e screws 83 to position theplate concentri'c'ally; and then tightening the screws 84 to lock' the plate in position," all likelihood of the plate becoming misalined with respect to'the spindle [3 may besubstantially eliminated. At

times when such an operation may be required. V

The marginal portion of the plate 80 terminates a" short distance from the inner wall '"of e the upstanding flange-I2 of the housing H, and is adapted to support a'measuring cylinder86. The cylinder 86 is'relatively short and of such 'inside' diameter as to receive the plate 80, the

outer diameter of the cylinder being, of course, less than the inside diameter of the flangef'lZ. The cylinder carries an inwardly directed, an-

nular flange 8'! at a 'point'substantially midway betweenits top'and bottom spaces. The'flange '81 extends inwardly from the cylinder a distance suflicient to permit its engagement with the outer marginal portion of the plate 80, so that the cylinder is supported in position upon said plate by the engagement of said flange with the plate. "A double scale, calibrated in degrees, extends clockwise fashion around the periphery of [the disk as viewed from its upper side. Asecon'dscale 89 (Fig.' 8) is disposed upon the lower portion'of 'thecylinderfand extends around the same in a et slr ntsa d gw zl le i 9 h l p e s le. fiat-m r be. ethan d e ht-hand S a e: en ear h viewd h r a uf i fihe fla e pen d f the l 'oi s i i0 n nsi. i The lower, or left-hand scale 89, is viewecl through lac-s m n ws?e t ithafi "k a 'ii lit to state that they provide for 'fiialii'nga roiigh readingfcf the angle being obd fror the biirpose of detrrniri'i g the appr x ijr'late magnitueeer the within acc" ay oi ofie-hal'fota degree! measuring- 'gie's to the eft; the,

14; will be viewed throii h the left h 1 dow'; 'siniila'rlyjifi rheasiirifigfari st in lglity therright-hand scale Will he'vie ed th ugh the .-hanfd window. thi I ner'; fa spa 'sil'ibjective error wmen dfftfi 'ocb'ur dr, from engagement with, the Flat/d and tn reby permit itsr'otatiohwith respeet hereto,

whee, ncludes "pair orwidefi 'disifio'sed. flippersffiii adapted to engage beneath the.lint/"er tag-eerie the cylinder}; 93a

irtehdir'ig laterally threfrd' teribrlyof the ho'ii's'i'ng 'w so. o'fi'erable from the vexterior. hr 611 This same clvi's also carriesan inte 'rod IEO projecting toward nthedoppcisi Thesecondflelevi's carries an integral to "H .projecting toward the bar H10 arid Y1 en er end telescobed y tog'g nsleve suitableisp'iring 1031s compress inner end 0f the sleeV I02 and 2 step I04 harried by the bar [0! so as to urge the sleeve I02 con- "stantly outwardly with respect, to the bar. lfll.

The outer end of the sleeveis notchedand receives a transverse "pin I05 provided inthefoiiter end Of the toggle rod l 00. Dlle t0 the inflfih e or the spring 103, a togglev actionis acmevedw 'i'ch causes the .clevise's 91 to assume either a convergent or a divergent position. In "subh "pbsitiens,

, 1V 42; I.\; the e 96 a eit a ne he em ne th fii r fefit. t tl either raised or lowered. J Sinceon'e ofthe'cl be n a y ewe-ted fk in' enf i or arm 39, and s ich rota} 've movement is, transniitted to the opnojsite cleyis means 'of the n; gaging toggle bar toggle sleeve, said opposite clevis is also caused toinote atthesame title the first named clevis is inoved. This} an ii fa 1 ment is provided which 'rirniits the siniultaiieoiis raising or lowering of theffiipfiers 9J3.

As is clearly shown l0 and 1 1; the outer extremities of the flipper tare position'edadjacent the inner wall ofjthe marginal flange fit of the housing iii. In this liositiomthe flippers, iinde'rl'ie the lower edge of theh ea's v g cylinder '85 and may engage the same upon iipwardmovement, In the lower position of the fii'piir's, the cylindeigis allowed to rest upon the inner surface of the plate 89. However, upon suitable actuation er the arm 99,. the flippers are caused to lift or raise, thereby engaging the bottom edge core the cylinder 86 and raisingsaid cylinderfroxri engagement with the lateau The flippers 9 3 are secured to and rotate with the housing W so that the cylinder 85 iscaused to rotate with said housing when it is lifted from, the plate 80 and supported solelynpon said ,flipp ers. ltisto be noted that this vertical movement is not sufiicie'ntto remove either of the scales 83 39 from the field of observation through thewindows Si) and 31. In this manner, the scalesmaybe read ,whether the cylinder is in its upper or its lowe1 ;p0 sition.

The upper side of thenoi jsing 10 i closed by a suitable, transverse, circular 'plate 719 6 which may Jpe sequred to the housing in any s itable or desirablefashionh The plate H16 e tn e gnar gma1, dependi fl 61, .snaced, i wa d tl Ia sli distan e rom t nr l er rm and adapted to engage snugly Within thedi 'upperj, orilower ,positions ct cylir' derl, I

As before pointed out the meas'iirihgpyhflde'r 88 intakes li'ovilsion only for the, reading of an observed angle to a fraction ar ag dlegree. 0 t fifs sirab e, i c urse to. m l thi.. '1 title as clo'sely and accurately possible. v For this r asq elplat 8. s rovided i ra ny extending ihdi'cia I0 8 arranged than, anniilfis ti s, iph y n pa ed s ight away therefrom. flhe indic'ia iOBQoonsists for alternate n XJ i 16.8! a s q indk lie [0812 the spacing between vadjacentshort and long d x, s rese tin one degree},

An opti eal system is provided for reading the interpolating the annularnindex lflsu The 'ysm v1 b: theghonsing 'mwrh 'opehm 's j flfinnfider i the mar inal ignition or the, tra sparent m asur n plate!!!) ing 10', as viewed 1h Fig; 9', a reflecting and then enter the eye piece H3.

, arrangement, the observer receives a multiple image, the lower portion of which represents the right-hand section of the scale I08 while mirror I I is carried upon a bracket III depending from the under side of the cover plate I06.

recited above. However, each scale moves in opposition "to the other scale no matter 'in A suitable lens I I2 is also carried by the bracket I II and directs light passing throughthe lefthand opening I09 and the left-hand portion of the scale I08 upon the plate 80 onto the prism IIO, the latter being so positioned as to reflect this light transversely across the upper part of the housing in a substantially horizontal plane.

I Atthe right-hand side of the housing, this light enters an eye piece II3 carrying a lens II4 so that an observer may view the left-hand portion of the scale I08 as revealedby the light passing through the left-hand opening IIlQJ A second bracket II5 depends from the under side of the plate IIlB at the right-hand side thereof, this second bracket project-ingdownthrough the right-handiopening I09 and the right-hand portion of the scale I08. The prism IIB directs thelight so received in a'substantially horizontal plane toward the left-hand side of the housing, said light passing through a 'suit-' able lensIII afterleaving the prism IIB, the

lens II'I being provided for the usual optical purposes. thelight coming from the prism II6 strikes a plane mirror lI8 rotatably mounted upon a de- Near the center of the housing Ill,

v reflects the light rays back toward the righthand side of the housing 10 where they pass through a positive correction prism I positioned above the lens lI'I on-the bracket II5, With this the upper portion of the image represents the left-hand section of the scale I98. The light coming from the prism IIO passes over the top w of the deflecting prism I20, while the light comshadow cast by the upper surface of the prism I20. This line appears in Figs. 20 and 2l,which represent samplereadings or observations as viewed throughthe eye piece I I3.

The transparent measuring plate 80 is fixed with respect to the tripod (not shown) upon which this instrument is supported. Hence, the plate does not rotate with the instrument but remains in a set position. Since the plate carries no numerical indications of angles, but only line indications of degrees, this latter fact does not lead to any confusion. However, as the housing is rotated in a clockwise direction (viewed from above), the upper image in the eye piece, representin the left-hand section of the scale I08, will appear to move to "the left.

At the same time, the lower image, representing the right-handsection of the-scale I08, will 'appear to move to theright. Thus, the two scales or images appearing in the eye piece appear to move in opposite directions as the housing is rotated. Similarly, when the housing is rotated in a counterclockwise direction, each of the scale images appearing in the eye piece willapwhich direction the housing is rotated.

' This phenomenon is utilized to obtain very accurate reading of the angle through which the housing has been rotated. Since the scales, the lines of which are spaced apart one degree, are simultaneously moving in opposite directions whenever the housing is moved, any "one index line, for example one of the long lines l08a, moving across one of the images appearing in the eye piece will alternately come into register with long and short index lines appearing in theopposite image each one-half degree of rotation.

Since the amount of rotation between consecutive alinings of any one index line with two adjacent long index lines in the opposite image represents one degree of rotation and the amount 'of rotation between consecutive alinings with 'adjacent long and short lines is one-half of a degree, a reference index is provided for giving an indication of how far past or how far short of an even degree or an even one-half degree the housing has been rotated. The meansfor reducing this indication to an actual, definite reading is I, described hereinafter.

This modification of the invention is provided with a clamping ring I2I, similar in all respects to the ring 42 and having one side split and formed into radially projecting ears I22 through which a screw-threaded bolt I23 extends. The outer end of the screw I23 is connected through a universal joint I24 to an operating rod I25 which projects through the bottom II of the housing I0 and carries a knob or handle I26 upon its outer end. These elements recited are similar in all substantial respects to those previously described in connection with the clamping ring'42. By turning the knob I26, the ring I2I may be clamped upon the lower portion of the washer 15, or may be loosened with respect thereto. The

. ring I2I carries a radially projecting arm I2Ipositioned diametrically opposite the ears I22 and extending to the marginal portion of the housing, at which point it projects through an opening I28 in the bottom H of the housing and has its outer end engaged by a spring-pressed, adjusting, tangent screw I29 similar in all respects to the screw 53 previously described. Also similar to the screw 53, the tangent screw I29 locks the clamping ring I2I to the housing while at'the same time permitting a small degree of very accurate adjustment between the two. I

In carrying out observations with this modification, the arm 99 is actuated to lower the flippers 93 and cause the measuring cylinder 86 to come to rest upon the upper side of the measuring plate 80. In this position, the cylinder is immovable with respect to the plate and the tripod to which the plate is connected. If a left-hand angle is to be measured, the housing is rotated, after loosening of the clamping ring I2I, until the cross hair 92 in the left-hand window 9| comes into exact registry with the zero line of the lower scale 89 appearing upon the periphery of the cylinder 86. Normally the cross hair 92 of the right-hand window 90 will at the same time be broughtinto registry with the zero line of the upper scale 88. v

to the housing. After this operation, the housing is rotated to bring the telescope I30, connected therewith, into registry with the first point of ob parently move in the direction opposite to that 7 servation. It is to be noted that the cylinder 86 ene 'ei n i lies tiefi 'i' t ft i f h theme ring'platef3fi'which'isfconnecte "aid rs no' pa'rticular relationship wi k t the first point'oi observationfit most c when'thetelesoope hasbeenalined h"s;aid po1ntfthat' the indicia er; theplate *ae j hich' ap'pear "in the upper and lower imagesin 'e eye 'pi'eoe l l3 f are notalined as viewed in'sa'id ye ece. t "desirableto have su'c hi eia Vida? a fixed "starting"point,'andf it fi s iorthis frea'sonthat the'mii'rorf l liiis pivotally jimoiinted 'upon the'bracl'ret l l 9. For permitting ee re i a u tm t th .n i f t s lower tion 113 l ojfthebracket H9 is fefiset-toone t e 'thejrnirror"pivotally -mounted upon-said 'rofiset'portionby meansbfia vertical p tending upwardly from "the portion l3 lnough"thefbodywfsaidmirror. *The lso'l'darries jj a"laterally'extendingarm l sewmch rojectsfhorizontally to af point adjacent the oiiterfpo ion of the housing iii. "A' spring f'pressed lun'ge "iscarried in'a'hoiising (35 dependng from the" undenside of" the" cover "plate 106, rand'saidplunger engages one side of the" arm .j. "[33. Thai opposite sideof the" arm" "is engaged 'sib he. i ner n M "an? a u in nge t 'qr If I 36 "extending horizontally with respect "to the l housing and engaging in a screw-threaded boss "-i'l 3Tfpositioiied" at one side 'of the "housing. FBy justing' the screw I36, 'the 'riirror *Hiifniaybe 'i causedtdpivot about the'pin eg nd thus- 'ehange the angle" of reflection of the flight rays-"striking 'jr said mirrorifromthe prism H5. By employing fthis structure, theindex linesfofthe upperahd Q ower ge fappearing int'he eyepieee I -L' i' may be "fbrouf h*' nto jexact and 'iaccurate' unemena i so as to" rov de a'fiXed startingpointfrom-which to mal cej "observations. From thisypoint enw'ard in 'jthefprocedure; fthe'" position of tl en'rirro r is not altered, since "to do so would incorperatean ""i'ndeterminateerror inthe final readin bt a'ri'ed.--v At this "pointfinfthe" operation; the-z er "bf the cylinder 85 have been" aceurately and exactly alinedwith" thejfirst'point of observation. It is to be noted that the accuracy of setting or f i i i i I in the finitialf step" recited hereinbefo re is' {not if rtieularly critical since the aliner'rlenti of the ,findesa mesiab'pearin n the" eye piecejH 3- isfrelied upon for the"required acciiracy andthe scales fgiying afreading [of the observed anglewithin ej e 'i ne e r s. W i .Heii e i ".h "'m c ra f mntffwith theseondpeint"of observation. rt :clamp'ing ring IZI is now ?tightened on-see; ed "and the tangent jsc'rew; I29 again employed' to bring the cross-hairsof-the telescope into exact aline'm'ent "with the "second'point oi -observation.

Having made such-*al inement, the approximate observed angle may be read througheit-her of the 'windowsto or-Blfidepending upon whether a right-hand or -left-hand' angle is being observed. Howeverg-upon observation-through the eye piece I I3; it will almostinva'riably' be found to' be 'the case that the indexlines' appearing in the ripper and lower images are' not in ali-nement with 'ene another unless by *pure coincidence the angle "measured" is exactly an even; degree or nuinber "of degrees. It is in--providi-ng'--accurate means appears to move to the right. "converselyfithe scales move in opposite directions when {the housing is rotated in a "left-hand or counterclock- Wise direction. Keepi'ngthis fact-in mind,"-' '-'the observer will know uponlookingthrough the eye piece whether the instrument has'been -rotated less than 'or moire than 0ne-ha1f--'of--6ne degree past the last full degree of- 'rotatitin fin moving to the'second'po'int inf-observation. liig. 20 'of the drawings m'aybeemployed to illustrate this point by assuming'the scales appear as represented in this figurea fter -h aving ineasured a right-hand ang1e.- sin'ce the upper scale is known to move to the le'ft-and'the lowers'cale to the-right, a comparison of the long index lines 1 08a -sh'dws that the instrument hasbeen revolved past-the last full "-degreef'but not quite one-half'ofone degree past "such point. This factmaybe recbgnized from the realization-that continued rotation to the right must be effected before the long index lines l fiea'in the upper: image come into alinement "with the short "index; lines I-OSb in the lower image. The observer is therefore =fi1rni'shed with the information -that-a small additional' angular measurement-of less than thirty minutes must-be determined to "completethe small additional measurement-must be added to the rough" angular :reading 'fobta'ined from-'the A H p h A v Vmeasuring cylinder"'-8fi. For-the purpose 'of furjthecrossfhairs 'filwith sa id zero lines trier" illustrationfand assuming that a left-hand angle has been measured; the observer can "determine at a' glance from the indications illus- 'trated in'FigZO that the instrument has been rotated more than thirty" minutes *past the l'ast full degree of angular-measurement. 'Ihis isobviously truesince'the long index-lines 68a in the upper image-have pas'sedthe short index-lines I081) in the lower image in-the course' of their right-hand travel, and thatless than one-lialf degree additional rotation is required -to again bring the long index-lines (08a of the upper and lower images into aliner'nent.

An 'optical wedge "or-prism" 1-38 is provided for the purpose of causing the index lines appearing in the eye pieceto' undergoappar ent moyement and become alined. The wedge [38 is interposed in the light- 'path-between the prism -HB-and the-eyepiece--l-l3 and dependsimm a -carrier pin 139 projecting through an elongate 17' is in verticalalinement with the aforementioned light path so that the wedge I38 may be moved to various points alongsaid path. Th pin I39 depends from a vernier carriage l4I positioned within an elongate vernier housing I42 provided on the upper side of the cover plate I06 and overlying the slot I 10. The housing is trapezoidal in cross-section and is wider at its bottom than the slot I40 so as to provide marginal surfaces I43 upon which the carriage I4I may ride. An elongate, square-threaded adjusting screw I44 extends lengthwise of the housing I42 and engages within a screw-threaded bore I45 extending longitudinally. of the carriage I4I. One end of the screw I44 is journaled in one end wall of the .vernier housing, while the opposite end of the screw extends through the opposite end wall of the, housing and carries a suitable operating knob: I46. By turning the knob I46 and thus the screw I44, the vernier carriage and the optical wedge. may be caused to mov longitudinally of the light path extending from the prism H to the eye .piece I I3.

Since the wedge I38 has its opposite vertical faces disposed at an angle with respect to one another, the wedge functions to cause lateral deviation in a horizontal plane of the light rays coming from'the prism IIO, whereby the rays are caused to strike the eye piece H3 at a certain definite point. However, upon moving the wedge closer to or away from the prism IIO, the light-rays are caused to strike the eye piece at different points although they are bent through the same angle, this being true since the distance between the wedge and the eye piece is being varied. The wedge thus furnishes a second means of adjusting the position of the index lines in the Upper and lower images appearing in the eye piece, such adjustment being in the position of the upper lines in respect to the lower lines because the wedge is interposed in the path of the upper light beam only, and does not affect the.

position of the lower image appearing in the eye piece.

Elongate, transparent windows I41 and I48 (Fig. 12) are provided in the right and left-hand side walls, respectively, of the vernier housing it, said windows being suitably sealed by strips of glassor any other suitable material. The strips are designated in the drawings by the numerals I49 and I50 for the right and lefthand windows, respectively. Upstanding ridges I49 and I50 are formed integrally with respect to the cover plate I06 and extend into the housing I42. on each side of the slot I outwardly of the marginal surfaces I43. The outer surfaces of the ridges are. in planar alinement with the outer surfaces of the vernier carriage MI and carry suitable scales I5I and I52 calibrated on one-half minutes and extending from zero to thirty with additional divisions being'provided beyond thirty for the purposes of accomplishing vernier readings. The left-hand scale I5I is illustrated in Fig. 18, while the right-hand scale I52 is shown in Fig. 22. As shown in these figures, the scales appear in the lower longitudinal halves of the window strips I49 and I50. The vernier carriage I4I carries a suitable movable. vernier scale upon each side, said scales appearing through the upper portion of the window strips I49 and I50. The left-hand movable scale I53 is positioned immediately above the left-hand fixed scale I5I while the righthand movable vernier scale I is positioned immediately above the right-hand fixed scale I52. The vernier scales are calibrated from left to right from zero to thirty, each division representing one second of angular measurement, it of course being kept in mind in connection with all of these scales that the angularity of the wedge I 38 is so selected that in moving said wedge from one extremity of its path to the other, the index lines appearing in the eye piece II3 are caused to shift one-half of one degree, or thirty minutes, with respect to one another.

Since the upper and lower images in the eye piece move in opposite directions depending upon whether the housing 18 is rotated to the right or to the left, the fixed scales I5I and I52 must extend ino'pposite directions. This is, of course, accomplished by the disposition of the scales on opposite sides of the housing I42. The movable vernier scales aresimilarly arranged so as to extend in opposite directions. Thu if the zero point of the left-hand, movable, vernier scale is in alinement with the zero line of the left-hand, fixed scale, the zero line of the right-hand, mov able, vernier scale will be in alinement with the thirty minute line of the fixed right-hand scale.

This is necessary since longitudinal movement of the wedge I 38 causes shifting of the upper image "in only one direction whereas in operation, during revolution of the housing I0, the upper image may move to the right or to the left depending upon whether a left-hand or a right-hand angle is being measured, and it must be moved a small additional amount to the left or to the right to effect alinement of the index lines in the eye pieceand thereby measure the small additional angle increment referred to hereinbefore. Normally, the right-hand scale is employed for reading right-hand angles, and the left-hand scale for left-hand angles although obvious variations in procedure and operation may be employed if desired.

At the beginning of the measuring operation, in the present instance, the right-hand, movable, vernier scale is positioned that its zero line is in vertical alinement with the zero line of the righthand, fixed scale. The zero reading upon the first point of observation is then effected and the mirror II8 adjusted to cause alinement of the images appearing in the eye piece 3'. 'The position of the wedge I 38 is not shifted during these steps nor in the latter steps until it is desired to take the final reading. As previously described, the cylinder 86 is initially positioned at zero and then fixed withrespect to the'im-.

movable'plate 80. At the sametime, the mirror H8 is adjusted to bring the index lines of the upper and lower images in the eye piece II3 into vertical alinement. Also as previously described, the housing is then rotated and the telescope I30 brought into exact alinement with the second point of observation, at which time a rough reading may be taken from one of the scales 88 or 89. At this point, the index lines of the images appearing in the eye piece are most probably not alined with one another. The operator then rotates the knob I46, thereby shifting the carriage MI and the wedge I38 longitudinally between the eye piece and the prism III. This movement is continued until the index lines in' the upper and lower images have been precisely alined with one another. Then, by taking a reading from the right-hand, fixed vernier scale,and interpolating this reading to further accuracy by means of the right-hand, movable, vernier scale, an accurate reading i had of the small additionalangle, or angular increment, required over 19' and ebmwihe de reenrlwho edeeree ead;- ins obtained i nit e scale 8. tno t inthe an le t .thehri w-m I na ality the ousin :nQ mov dndu inelt j s n .We sand themtelescopeerema ns, raine xa y; 1 9. th s o 'p int f lyser at pn- .M l Ihe movement t e ilwe eejl 3.8 ei seslthe up erv sca eiina e ounde eo appa e eil ltse movement and thuso an esu ppar nt ,r verse h t oi th musin hr uehthat. sma l additional amgllnl lover and'taboye the last wh 0le ee ee iim atiqn actua ity, this increment of .rp atiqnis.measii ceduvitho inm t makin such. rot tio i'amliqwev niby arbitr y, ection Qt th ive nier 's l s th scons rv d dat may b read ti 'lte msw f theui act pn joi the. obs ve an lefoyerlan .ahq zeithellast n qde ree. m kin ohse xat n j o ft-hand; angles. he v arn ed, (QLJXLQY beshifted to the oppo ite en .t .vh,Qu insi142; oreit m y' e iz ni helnqsi pnshqw in i' 18 andithe readine oo ainedl he eirom,v plus. 0.;m nutes, added to the nextlgwer degree as indicated in" the leftdl'uwi s pwlfl ljn r r e;n :99 dur loor .7 ineas rmeibqth r t; a

eiizhand an le .i'sthe: me. and the an lar at n hetw e -enrwo poin may e sidered s ei her; toe/r h .Qr;.. e. ti-i lithep n of he vernierjscale sis o n n/F 8 s s a a be nn n mint th vi nal V nier re o both right and left-hand' angles arepaddedto the negrtlowerhalf degree as indicated inthe windows lf gcare is lused in'j the "initial" setting of thegylinder it, should be "possible, to estimate whethenor nqtfa half idegree should badded'to' th .inezi 'fl ower. ,gltadyatidn ,in addition toithe Vernier reading. The relative "positions "ofthe' long toithe short graduations of:.the upl zrand lqwerinlages, as'illustrated' in' Figs. 20 and 21'; athpth beginning and finalireadingsfafe ai'posi tive guide as to whethef, toladd' 30 minutes "to thellvernienreadings Iri all cases'it"wo'uld be added; to one. of either"the ri'ght "or' left ar'i'gl andfnoVto the other. Both"the right'andthe left angl'e's'j for anyiobse'rvation may be read -by adding to thewindow readings thevrnir read ing-of theiscale observed'aboveit. It ispossibl to use theopposite end of 'thevrhierscale as a starting :point but the reading would 'still be added; Th/ruleffor addingflo minutestothe right or left reading from the position of 'long'to :1

short "graduationsiof "th'e'irn'a'g's would be reversed 'thi'sca'sef'a n"dit is probes-1e 'thaf'most' operators would prefer'to' alwaysusethe same posi tionio'f the wearers-ass startingbo'int foi" all cases.

optfoesiyfif the 'tl e's'coii' istr'aineaf pon one point and thenfiadtari ed to aseeoijid p'oiii'tthe final" result "would be the same whet er rotation The mechanical arrangement is such that if the i nages are matched upon the'initiailsetting with like graduations 'alined', or longwith' long" and shQrt With short, upon reael'i'ing'th final posii iQ iheoimages maybe al'ined by movement of heuw d euto register in" one of'the'two conditions ofialinement; like 01 unlike? vIf the" measure ment is an exact number of degrees they will] be like; if; an even :number "of *clegiees'wlus minutes they:willbe u1'1like." Since eitherwoiild seldom-he the case, the wedge is employed to deflect the upper image to effect alinem'ent: The arrangement gf-the wedge and-itsiverniergscales is selective" in that either the right *onrthe'left scalesmay'be initially "set on zero; This auto -i' matically places the opposite scale'oni 30 -0. If the rightiscale is set on zeroas in'Figf 8;anY sh'iftingof the, wedgeifrom this terminal position must: be in the direction that will efiectan increase in"the-'l'ight' residing from 39 0" and"a decrease 'in' the "left reading from "30 -0" This afiects the upper image 'irl'"such-a way that "it-is shifted in"'th'e"opposite direction to" its-"movement whenthef'telescope i's rdtated'tto" th'eTiglit? Simi'-" larly; if the- Wedge is set at*theopposite' end; of the scale it can? onlyhe" advanced? through tli'e increment of leftwardirotationf If; after shift ting the" position of the wedge ficmi' either 'ter minus to cause "register" of"the"-ima-ges" and-"like graduations'i'areialined," the increment is added to that angle that is in positive agreementiwith the 'initial'setting ofthe wed'g scales? If unlike graduationsare' alined "an "additional incre ment'ofBO" is added'totth'at angle. At the same time, since 'theopposi'te Tve'rnie'r scale would" have decreased in're'gister' fron'ia reading of- 30' which wouldh'av required an a'dditidnail 30 initially to coinpleinent thereadingof zero on the opposite scileof aIYactual' value of because the" next lower degree isobse'rvedinthe 'windows "9n "and 9]". andthetotal of theW'e'rni'i readingsfwheit added to the total "of 'the'windoiiv readings"; must equal 360? Therefore, thereading -offthi's""op'-" posits Vernier lus30" w'oiild beadd'edtdthe'angle out Ofpos'itiv' agreeinent With-the setting-ofthe wedge'sca-le-irr the first casefa'nd its reading alone'ejdde'd m thesecond case; I

Thisdbtion xnai hecla'rified by 'a hypothetical" assignment"of po'sitive' values to movements eor: responding to" ri'ghtward rotation or the telescope and negative valiies" to those corresponding to leftward rotation. The cylinder, being indexed inbotnnirtio 'will eistef 'hbtha ositive and a" -'nea;'tnie -val for'any osition: The"wed }ge maybe sel elfs'et" to be shifted infeithei'fa'- ositive or n'e'g'atiije"directiononly from one or thef'othr' terminal pojs'itionsb it since its Vernier scjalesfruii 'oiipo'si't direlctiqh's they will reg iste'r'a'rea v'a ggr itsjbq'sitiori relative toeithei of,"'bo'th"a os'itive aiidng'tive value: If the initiersettm of v dgeji as in Fi 3; the effector v] ement upon the upp'e mage w'nr'benegatii' eh the realmeasurement oi its" mf emenffwillj register onjthe' right Vernier scale The miner-3'0" reading off thelft Vernier scale isoiiegbbrl'giriQlYreduced by the'jsame Value."

-* ine t or the" edge to register under the' opido'site sign 'oth'aittlie right "scal registers the meremeh to eadde rtq the right reading of the "thea'ctual aniodnt by'whi'ch outer regist r before theyW'ere righti krardljir ucd and leftwaidly 'increased to brin' abffut registry. I w I I To summarize; if the Vernier scales 'areinitiallj sa es g: 8 andtheinitial and entree" of 'alir iement are the time"; the right jrrriifscale' reading is added td'tlie' right cylinder 'seaieread 21' initial setting of the vernier scales is opposite to Fig. 8, the 30 increment must be added to the opposite angle in both cases since it registers its real value on the left or negative scale.

Figs. 18 through 23 illustrate the appearance of the various scales in the course of making actual angular observations. It is believed that the mechanics of operation of this system will best be clarified by a recitation of the steps and operations in making observations of a right and left-hand angle employing the same two points of observations so that said angles are complementary. To begin with, Fig. 19 represents the appearance of the right-hand scale 88 as viewed through the right-hand window 90 after the telescope has been trained exactly upon the second point of observation. The cross hair 92 indicates the observed angle to be something more than 35 but less than 36. he indication is also that the observed angle is less than one-half degree greater than 35, but such indication need not be particularly relied upon for an exact determination of the observed angle.

Fig. 20 is a representation of the indications appearing in the eye piece H3 before the prism I38 has been moved to bring the upper and lower index lines into agreement. Keeping in mind that a right-hand angle is being observed and that the upper image is therefore moving to the left, an examination of Fig. 20 will disclose that the housing has been moved less than one-half of one degree past the last whole degree, this indi-- cation appearing in the fact that the upper long index lines 38a are only to the left of the last lower long index lines I03a, but not to the left of the next short index lines [88b in the lower image. This shows that the long upper index lines IOSa have moved to the left of, or moved past, the long index lines but not the short index lines in the lower image. Therefore, at the outset, the observed angle is known to lie between 35-0 and 35-30'.

The vernier scales and the optical wedge I 38 are now employed to bring the index lines back into agreement or alinement so as to determine the small additional angle through which the housing has been rotated past the last whole degree. As previously described, such an adjustment is effected by means of the screw I44, the latter being rotated by the knob I46 until the wedge I38 has moved into such a position as to bring the upper and lower index lines into agreement, as illustrated in Fig. 21. After such adjustment has been effected, the vernier scales will appear as illustrated in Fig. 18, and the. small additional angular increment may be read directly therefrom. The reading illustrated is 8', plus less than 30" since the zero line of the movable vernier scale has not passed and is to the left of the half minute indication on the fixed scale, plus 16", the interpolated figure obtained through a reading of the movable vernier scale in the usual manner. The total observed reading is thus 35-08 l6".

As previous pointed out, the angle between any two points of observation may be measured as a right-hand or as a left-hand angle since the resultant readings will be the same regardless of whether the telescope is rotated to the right from the first to the second point of observation, or whether it is rotated to the left between said points of observation. Assuming the same two points of observation as employed in the immedi ately preceding example, but also assuming it is desired to read the left-hand angle rather than 22" the right-hand angle, it is obviously immaterial whether the telescope was'rotated in a right or a left-hand direction in order to become exactly alined with the second point of observation, but it is helpful to assume for the purposes of determining the left-hand angle, that the telescope was rotated in a left-hand direction. Under these circumstances, it is to be kept in mind that the upper image appearing in the eye piece will appear to be moving to the right as the telescope is so revolved or swung. Fig. 23 represents the appearance of the left-hand scale 89 which appears in the left-hand window 9| and displays a reading of between 324and 325. A close examination of the figure will show that the angle to be observed is greater than one-half degree more than 324. However, as previously pointed out, this indication alone ned not be employed to determine this fact since the images appearing in the eye piece I I 3 will settle the question beyond any doubt.

1 Figs. '24 and 25 represent the indications appearing in the eye piece I I3 before and after the prism I38 has been adjusted. in order to aline the upper and lower index lines IBM and I081). Fig. 24 displays therelation of the upper and lower images before such alinement and is, of course, identical to Fig. 20 since the telescope is exactly trained upon the same second point of observation as employed in connection with said Fig. 20. Indeed, it may be that the telescope has not been moved at all since the observation of the right-hand angle, the assumption of rotation of the telescope to the left in order to come into alinement with the second point of observation being made merely to clarify the steps of reading the left-hand angle.

I Remembering that the upper scale is presumed to have been moving in a right-hand direction since the left-hand angle is being observed, it will be apparent from an examination of Fig. 24 that the housing has been moved more than onehalf of one degree past the last whole degree, this indication appearing in the fact that the upper long index lines .Ili8a are not only to the right of the last lower long index lines mm, but also to the right of the last short index lines 1081) in the lower image. This makes it apparent that the long upper index lines IiJBa have moved to the right of, or moved past, both the long and the short index lines in the. lower image. For this reason, the observer knows that 30 minutes, or one-half degree must be added to the reading of 324 obtained from an examination of the scale 39 which shows the next lower whole degree to be 324. Y

I The optical wedge I38 is again employed to bring the index lines back into alinement so as to determinethe small additional angular increment through which the housing and telescope have been rotated past the indication of 32430 obtained from'the observation of the scale 89 and the initial indication appearingin the eye piece II 3 as illustrated in Fig. 24. In making such adjustment, it is to be noted that the upper scale is apparently caused to move to the right which is the same direction in which the scale was moving when the housing was being rotated in a left-hand direction. This small additional movement therefore represents the angle which must be subtracted from the next whole degree, or next half degree, in order to obtain the true'left-hand' angle. However, as previously described, the zero line of the lefthand movable vernier scale I53 is alined with the 25 lar to the plate 80, aflixed thereto by screwthreaded bolts I14 and 'being positioned by adjusting screws I15 similarly to the plate 80. The plate I13 is thus disposed in a vertical plane within the housing I62, and being secured to the washer HI and the shaft IBI, is adapted to rotate in a vertical plane with the telescope I30. A clampin ring I16 encircles the inner portion of the washer HI and carries a laterally extending adjustin arm (not shown) adapted to be adjusted with respect to the housing I82 by a suitable tangent screw I11, similar in all respects to the tangent screw I28, previously described. A clamp operating rod I18 extends through the annular wall I01 of the housing and is adapted to tighten or loosen the clamping ring upon the washer Ill. The shaft I8I, and therefore the telescope I30, may thus be securedto or released from the housing I62, or they may be minutely and accurately adjusted with respect to the housing by means of the tangent screw I11.

This vertical angle'measuring system does not incorporate a measuring cylinder similar to the cylinder 86, but instead carriesv an additional scale or scales upon the plate I13. This scale, designated by the numeral I19 may be viewed through a window I80 cut in the upper portion of the cover plate I65. The scale I19 is divided into a clockwise and a counterclockwise scale, each extending from zero at one side of the plate to 180 at the diametrically opposite side'of the plate. The scales are displaced 90 with respect to the longitudinal axis of the telescope so that the operation of the horizontal angular measur-- ing system, the scale I19 is employed merely to obtain a proximate reading of the observed angle, such reading being accurate only to the nearest degree. For the purposes of exactly determining this angle, an optical system is employed which is substantially identical to that employed in the horizontal system and has been designated by the same numerals in the illustration of the vertical system. The prisms H0 and H8 are employed in the same fashion, and the adjustable mirror II8 with its adjusting screw I36 and the optical wedge I38 being employed in the same manner and being arranged in asubstantially identical fashion with respect to one another. A similar vernier carriage MI and the vernier carriage adjusting screw I44 are employed, but a slight modification is made in the housing for the vernier carriage. This housing I8l, is rectangular in cross-section and carries only a sinle window I82 upon its outer side. The window exposes a fixed vernier scale I83 provided above the carriage I41, and a similar, fixed, reversed, vernier scale I 84 below the carriage. A double, movable, vernier scale is provided upon the outer surface of the carriage I4I' so as to be disposed contiguous to the upper and lower scales I83 and I84. The movable vernier scale includes an upper scale I85 for use with the upper scale I83.

, 26 and a reversed lower scale I88 for use with the lower scale I84. This vertical modification is further altered in that the eye piece 3' carries a reflecting mirror or prism I81 which reflects the images received from the prisms IIO and H6 at right angles into a laterally extending eye piece tube I88. This structure is employed since it is not always convenient or practical for the operator of the instrument to view the images provided through the annular side wall of the housing I84. The housing is disposed relatively close to the telescope I30, and an eye piece extending from the annular wall I61 would be too close to the telescope for practical use. Hence, the employment of the prism I81 and the laterally projecting eye piece tube I88.

v The vertical angle measuring system is employed in substantially the same manner as the horizontal angle measuring system. The initial setting of the proximate scale, which appears upon the measuring cylinder 86 in the horizontal system, is not necessary since the zero line of the scale I19 is arranged to appear in the window I80 when the telescope is in its horizontal position. When angles are being measured as above or below the horizontal, this fixed starting point may be employed with facility. Of course, if additional scales are provided for measuring from the zenith, the latter are used as a starting point when such observations are to be made. The housing I62 is provided with light-admitting openings I89 disposed at diametrically opposite points and adapted to pass light through the plate I13 to the prisms H0 and H6. The plate I13 carries a scale, similar in all respects to the scale I 08, and interposed between the openings I89 and the aforementioned prisms. The images of this scale which appear in the eye piece are employed in the same fashion as previously described, and the mirror H8 and wedge I38 employed for adjustment in the same manner. The upper vernier scales I82 and I85 are employed for reading positive or upwardly directed angles,

, while the lower vernier scales I84 and I88 are employed-for measuring negative or downwardly directed angles. Of course, if it is desired to measure an angle from a point above the horizon to a point below the horizon, both theupper and lower angles may be measured and added, or the telescope may be set upon one point and the scale indications brought to an even degree by suitable adjustment of the mirror I I8. Then, upon swinging to the second point, the final reading may be obtained through adjustment of the wedge I38 and the initial reading added to this second reading, the second mode of operation being preferable in that fractions of degrees do not need to be added and that some operational steps may be eliminated. I

In Fig. 15 is shown a schematic diagram of the optical system employed in both the horizontal and vertical angular measuring systems. The right-hand light beam which will be designated by the letter A, passes upwardly to the prism H6 and is reflected through the lens II1 to the adjustable mirror I I8; From the mirror, the light ray A is reflected back to thefixed correctin prism I20 and thence through the lens II4 into the eye piece 3' to provide the lower image in said eye piece of the right-hand portion or section of the scale I08.

The left-hand light beam B passes upwardly through the left-hand portion of the plate and therefore the left-hand section of the scale I08, through the lens I I2 to the prism I I0. From 27 the prism, the light beam B is reilected transversely across the instrument, passes above the mirror H8 and strikes the adjusting-prism or optical wedge I38. This secondlight beam isdefiected by theiwedge I38 in passing therethrough and extends above-the fixedwedge 120 to the-lens H4. From the lens H4 the light beam B passes to the eye piece 1 l3 to providethe-upper image appearing therein, said'image representing the left-hand portion of thescale H18. Themirror H8 provides means for adjusting the angular path of thelight beam Aas itis reflected transverselyof the housing,,-while-the optical wedge I38 provides-means for-deflecting the transverse path of-the lightzbeam i'B. ."It is in the utilization ofthese-two means,*coupled with the novel scale ['08 and the Vernier reading mechanism, that many *of the advantagesof 'this'invention reside,

I aswell-asin the'proiris'ionofthe non-rotatable connection between the measuring plate im-and the support. 3

The foregoing description of the invention is explanatory thereof and various-changes in the size, shape and materials, as well as' in the details of the illustrated construction mayibe made, withinthe scope of the'app'ended claims, without departing from the spirit of i the invention.

-What 'I claim andtdesire-to secure-by Letters Patent is:

1. An-angle measuring instrument including, a fixed support, a movable 1housing-carriedby"the support, a transparent horizontal jangle measuring plate in the housing secured'to the support, a telescope mountedfor-swinging in a vertical'jarc upon the housing, a casing carried by the housing and afiixed thereto, a transparent vertical-measuring plate in the casing secured tothe telescope, indicia on the horizontal 'a'ngleimeasuring -,plate and the vertical "angle'm'easuring platefboth-the housing and the casing having anopti'calmeasuring system including; .means'for 'passingbeams of light through two*portionsoftheindicia carried by each plate, an eyepiece for each pl'ate, means for directing'the two 'beams-"of'lightior each plate into the eye piece for thatplate'so as to cause twoimages of said plate in'dicia to appear in'each'eye'piece, an adjustable'mirror for each plate for shifting one of the images appear-' ing in theeye'piece of that plate,and 'anadjrist able prism'for each "plate for shiftingthe other of the images appearing inthe 'eye piece of that plate, said mirror and said prism'being adjustable separately and independently of one another.

2. An angle measuringsystem including a mov-, able support,'a fixed support, an annularscale member for indicating the approximate angular position of the "movable'support, said member carrying indicia, means for observingone .portionof said indicia in afield of observation, means for observing a second portion of saidin'dicia the field of observation, a' prism interposed in the course of the "light passing to'thei field of'observation from oneof said portions for changing the course of said light to cause the observed portions to become alined, in one position'of the mov- 6 able support, an indicia carrying scale carried by the movable support, a scalereading device rigidly affixed tothe prism .and.movable therewith; "and a .mirror interposed in the course of the. light passing to ,thejfield. of observation from the .otheriof said portions for changing the course of'said light, so as to cause the observ'edportions to become alin'ed in 'another position of the movable'support; whereby adjustment of said'mirror results in alining of the observed portions of.v the annular scale member indicia without necessitating. the'movement of the prism.

An angle measuring instrument including, a fixed support, afixedjm'easuring limb secured to the fixed supportiandhavingjan annular scale graduatedinto angledefining-indicia, a housing rotatablygmounted ion the support, a telescope Jcarriedbythe housing and rotatable therewith, a secondjmeasuringlinibrotatably carried on the support "and rotatable'withgrespect to the. housing," the-second'measuringflimb having a scale graduated into angle defining indicia, means formin a part of the instrument for reading the second measuring limb scale, and meanscarrie-tl byrthe housing forreading the fixed measuring limb'scale, Whereinlthejmeans for reading the fixedmeasuring limb scaleincludes, an eye piece, an optical. system for directing beams of light fromtwospaced portions 'of'theilatter scale into the eyepiece, separate independently adjustable optical elementsinterposedin the two light beams for deflecting saidlight beams individually and separately, and separate independently adjustable. mounts carryingithe adjustable optical elements.

4. An anglemeasuring instrument as set forth in ,c1aim,3,.and a reading scale'on one oi'the mounts.

J5. An angle measuring instrument asset forth in claim}, wherein one of the adjustable optical elements is a mirrorand the. other is a prism.

.6. An angle measuringinstrument as set forth in -claim 5,, a reading scalecarried by the housing, and a .vernier. associated with the reading scale, .the .vernier and prism being rigidly connectedv together. to form an integral Vernierprism unit.

- IRWIN L. CUNNINGHAM.

REFERENCES orrED The followingireferences are of record in the file of this patent:

Number Name Date 774,515 -.Geier "Nov. 8;1964 1,502,223 Abraham July 22,1924 1,754,872 Bakeret al Apr. 15, 1930 2,221,317 .Wild Nov. 12, 19 20 2,363,877 Larsen=et al Nov.28,' 1944 2,480,237 Goodfrey et al. Aug; 30,1949

FOREIGN PATENTS Number Country Date 23,648 'Great Britain -Dec.'22-, 1392 246,650 *Great Britain Feb. 4, 1926 759,485 France Nov/l6, 1933 377,619 Italy Dec. 23, 1939 

